Friday, September 26, 2008

Overwintering Tender Plants, Part II

an overwintered caladium

In my experience, plants that overwinter well indoors are mostly tender perennials, bulbs, tubers, and shrubs often treated as annuals in climates where they're not hardy. These include many begonia varieties, heliotropes, fuchsias, caladiums, elephant ears, angel's trumpet, tropical hibiscus, jasmine, flowering maple, tender ivies and vincas, Diamond Frost euphorbia, dahlias, ornamental sweet potatoes, cannas, calla lilies, and too many more to list.

The first step when considering whether, or how to overwinter the many tender container plants here was planning. With mostly hardwood floors, due to the number of plants I wanted to bring in, I was reluctant to overwinter most things in our living space. So last fall well before the date of our first average frost, I splurged on a large sodium grow light for the basement. Grow lights come in different sizes depending upon the size of the space you wish to illuminate. This was an expensive and carefully-considered investment I plan to use for years to come. It was far less costly than building and heating a greenhouse or sunroom. (Not that I'd mind having either or both of those, but they're not in the budget anytime soon.)We have an unfinished basement - a good spot to install the light. It paid for itself the first season because of all the plants I conserved and propagated. For you, it will depend upon your budget, how many plants you want to save and/or propagate, whether you have a greenhouse, sunroom, or other space with enough natural light and floors conducive to indoor gardening, or whether you have a space in your home, such as an extra bedroom or a basement, where installing a grow light would work. Artificial lighting isn't necessary of course - sunny south or west-facing windows are great for all but the least sun-tolerant plants, while north and east exposure windows will be fine for the shade lovers. Protect windowsills and/or floors from water damage with non-porous saucers, and water carefully to avoid spills, leaks, and splashes.

Many plants can be allowed to go dormant and overwintered in an attached garage with only minimal watering - once a month or so will suffice for most plants. This works well especially with tender shrubs and tubers, and even some potted trees, as long as the temps in your attached garage don't go below the plant's minimum requirements. Since I've never kept a thermometer in the garage or determined how warm it stays on the coldest of the cold winter days, and since our garage is already pretty overstuffed, I decided to stick with the basement for now.

Our grow light costs about $10/month to run, and a replacement bulb costs around $100. In my case this means after my initial purchase I still save considerable money on plants in the spring, especially since I also use the light for propagating, seed starting, and overwintering perennial and shrub cuttings started in the fall whose root systems otherwise might not be mature enough to survive our harsh winters. Our sodium light is good for an 8' x 10' space, which I managed to fill with no problem.The light assembly is installed on hooks screwed into the exposed joists of our unfinished basement. It's suspended from adjustable cables for raising and lowering, and is plugged into a separate ballast unit, which is raised off the floor to prevent damage from the seepage we sometimes have in our basement following heavy rains (such as the one we just experienced when the remnants of Hurricane Ike blew through our area recently.)

Whether to purchase a grow light is part of the planning. You'll also want to consider which plants to overwinter. Some annuals are truly annuals, are easy, quick, and inexpensive to start from seed, and don't overwinter well anyway. Others, such as those listed above will usually be even larger and more beautiful, and bloom more their second, and even subsequent seasons if conserved over the winter. In my experience, caladiums have been an exception. They survived just fine, but were smaller and had less foliage their second season. I'm saving them again this year anyway. I did find that a good organic bulb fertilizer helped jump-start them, increasing their fullness and initially-disapointing foliage size. Even so, the new ones were still larger. Mixing some new bulbs with some overwintered ones was a good strategy for me. Since they went mostly dormant anyway after bringing them in, this year I may not bother putting them under the light, and will reduce watering. Maybe if they go fully dormant over the winter they'll come back a little stronger next year.

Coleus and double impatiens don't seem to be all that great either in a second season, but cuttings are easily rooted and grow fast. Just one plant can yield quite a few cuttings. Timing is important - I started the coleus cuttings early enough, but didn't think to start the impatiens until April. They were still pretty small by mid-May, so I did buy more double impatiens this spring. This time I'll probably start both the coleus and double impatiens cuttings in mid-to-late February. I'll let you know how that timing works out! Remember, overwintering outdoor container plants inside is pretty new to me, so I'm still doing lots of experimentation. So far though, I've been very pleased with the results.

A reality of overwintering plants indoors is the potential for pests and diseases. Planning ahead will eliminate or at least help keep these problems to a minimum. There are many methods of reducing and eliminating insect populations - some more environmentally-friendly and safer than others. The internet is a rich source of information on safe, natural, non-poisonous pest controls. Rather than promoting a particular method or product, I recommend doing some research and have a plan for preventing and dealing with any potential infestations. Even simply hosing down the foliage with a fairly strong shower on the tops and undersides of the leaves is helpful in removing many pests. It may take some experimentation to find method(s)/product(s) that work for you.
sweet potato vine overwintered last year

Knowing what they say about an ounce of prevention, you may want to thoroughly clean your plants and the surface of the soil before bringing them inside. Rushing plants indoors the evening before a predicted frost can be a recipe for bringing outdoor pests inside.

Finally, plan to spend a little time on routine maintenance and sanitation practices to keep plants healthy once indoors, and pests at bay. Basic sanitation practices for indoor plants can include an occasional lukewarm shower for the foliage, remembering to pay attention to the undersides of the leaves, removal of spent foliage and/or blooms from plants and soil, and sound watering practices, especially avoiding overwatering. Overwatering can lead to fungus, disease, and rot, and also can lead to pests, especially fungus gnats. Using sticky traps to both detect and control potential pests can be especially helpful, as is careful observation of your overwintering plants and knowing what to look for.

This series is inspired by Rose at Prairie Rose's Garden, who asked me if I'd post some tips on overwintering annuals. In the third post of the series I'll discuss a few more tips for overwintering and propagating plants indoors. In the meantime, I invite anyone who also overwinters tender plants indoors to add your own tips, expertise and experiences to the mix, either in the form of a post of your own, or comments here, or even better, both! A gardener's budget can be dramatically stretched by overwintering tender plants, and even propagating some of them over the winter.

double impatiens cutting started last spring in the basement.


  1. That's really interesting. The only thing I have overwintered are my geraniums and they do fine in a sunny window over the winter.

  2. I wish i had a basement then I too could save on money! We have a nice large sun room but those darn cats that I so love are my issue. I cannot forbid them in the sun room as that was the room I trained them to when they first came to us. So that is their room.
    Next house will have a basement or attached garage for sure!

  3. Linda, I am bookmarking this page so I can refer to it when I start bringing in some plants. So much great information here--I probably wouldn't have thought about pests or protecting the floors. Next week I had planned to clean the garage, but now I think I'll start with the basement first! I have the perfect spot for a gardening "nook," and I'm going to go shopping for a grow light.
    Thanks again for all this great info!

  4. Wow, what a wonderful idea! I've been considering one of those lights, but I can't figure out where on earth I'd put it. You always have such wise ideas.

  5. Hi Rosemarie, I had a few geraniums in the basement last winter too. They do overwinter nicely indoors, don't they!

    Hi Skeeter, I know what you mean about the cats!

    Hi Rose, I'm glad you're finding these posts helpful!

    Thanks Brenda!


Thank you for stopping by! Comments are welcomed, and while I may not always respond here, I'm happy to pay you a visit.

While comments are invited, links to commercial websites are not, and comments containing them will be deleted.

(Note to spammers: Don't bother. Your comments are promptly deleted. Hiding in older posts won't help - they're moderated.)